1. Field of the Invention
The present invention relates to a compact impact drive actuator which stepwise drives a slider.
2. Description of the Related Art
There is known an actuator that supplies a sawtooth wave drive pulse to an electromechanical conversion device coupled to a drive shaft to displace the drive shaft along its shaft to thereby move a movable member friction-coupled to the drive shaft along its shaft. Such an actuator is called an impact drive actuator.
The operating principle of the impact drive actuator will be described. The impact drive actuator has a piezoelectric vibrator whose one end is fixed to a stationary member and the other end is attached to a drive shaft. A movable body is friction-coupled to the drive shaft so as to be movable in the vibration direction of the piezoelectric vibrator. In such a configuration, a sawtooth wave drive pulse is applied to the piezoelectric vibrator.
More specifically, firstly, a gradually increased voltage is applied to the piezoelectric vibrator. The piezoelectric vibrator is then displaced and, at the same time, the drive shaft is displaced. The gradual displacement of the piezoelectric vibrator allows the movable body to be moved together with the drive shaft due to friction with the drive shaft. Secondly, a rapidly reduced voltage is applied to the piezoelectric vibrator. The position of the piezoelectric vibrator is then returned to the original position and, at the same time, the drive shaft rapidly returns to its own initial position. At this time, slippage is caused between the movable body and drive shaft, so that the movable body stays at the same position. By applying the sawtooth wave drive pulse including a gradually increased voltage and rapidly reduced voltage to the piezoelectric vibrator as described above, the movable body is moved from one point to another. When the above operation is repeated, the movable body can intermittently be moved relative to the stationary member. To move the movable body in the reverse direction, a horizontally inverted sawtooth wave drive pulse is applied to the piezoelectric vibrator.
An actuator that uses the above drive principle is disclosed in U.S. Pat. No. 5,225,941. In this patent, the impact drive actuator is applied to a camera lens drive mechanism. A movable body serving as a lens barrel is fitted to a drive shaft. Further, an elastic member having a bent portion is attached to the movable body at the fitting portion. In this case, the bent portion of the elastic member is brought into pressure contact with the drive shaft to generate an adequate frictional force.
Another example is disclosed in U.S. Pat. No. 5,589,723. In an actuator disclosed in this patent, a friction adjuster including a piezoelectric vibrator is used for a portion that generates friction. By synchronizing a voltage applied to the piezoelectric generator of the friction adjuster and a voltage applied to a piezoelectric vibrator for displacing a drive shaft with each other, an appropriate frictional force for a movable body to be moved is obtained.